Method and apparatus for neutral



r 8, 1953 c. J. CHARSKE 2,637,010

METHOD AND APPARATUS FOR NEUTRALIZING POLARIZATION HYSTERESIS IN CAPACITORS Filed Feb. 15, 1951 2 SHEETSSHEET 1 FIG. I. I

R; i c I SIGNAL APPLIED T0 CONTROL E E ENT 0F SIGNAL APPLIE ELEIE OF T l I I APPLIED T0 60 ELE ENT OF T APPLIED IENT OF T4 APPLIED T0 00 ELEMENT OF T.

SIGNAL DEVELOPED ATNODE 8!! R OFT AND T APPLIED T0 0 ID I 7 I I 2 7 APPILIED T0 GRID OF 8 POTENTIA MEASURABLE ACROSS CAPACITORS C AND C: s 4 I0 I0 2 2 I l I0 I 2I3 l o II t o 2 4 s 3 I0 I2 I4 I6 I8 20 22 24 26 TIME umrs INVENTOR. FIG 3 Charles J. Charske,

AGENT.

-2 SHEETSSHEET Z C. J. CHARSKE METHOD AND APPARATUS FOR NEUTRALIZING POLARIZATION HYSTERESIS IN CAPACITORS T T 6 mm 4 WC C J S J h k I k r I :22 dd M no .355 C "N @2150: f v. 1 B A LG 3 l I I I I I I I l I l I l I l I I l I I l 353 Q a mu n33 m a a G u 3 u h 8 W o m n .353 53.2 3 3.5m m2; .333. F @5263: n a O N 1 0 ve 2 k n vi a N G 1 QM V F April 28, 1953 Filed Feb. 15, 1951 Patented Apr. 28, 1953 METHOD AND APPARATUS FOR NEUTRAL- IZING POLARIZATION HYSTERESIS IN CAPACITORS Charles J. Charske, Houston, Tex., assignor, by mesne assignments, to Standard Oil Development Company, Elizabeth, N. J., a corporation of Delaware Application February 15, 1951, Serial No. 211,164

6 Claims.

The present invention relates to electrical networks employing capacitors having polarizable dielectric substances between the plates thereof. More particularly, the present invention relates to a method and apparatus for minimizing adverse eiiects attributable to polarization of dielectric materials employed in electrostatic storage devices which are subjected to repeated charging and discharging over small increments of time. In one specific form, the invention relates to improvements in electrical timing networks wherein the magnitude of the charge stored in an electrostatic storage device is utilized as a measure of time during which unidirectional electric energy is caused to flow in series from a source of constant potential, or constant current, through an electrical resistance and into said storage device.

Breily stated, my invention contemplates initiating flow of unidirectional electric energy into two parallel-connected capacitors. whereby a polarized electrostatic field is developed and dielectric material contained therein is sub ected to polarization by said field, term nating the flow of energy at the end of a desired interval of time, utilizing the potential of the electrostatic field built up in the capacitors, and subsequently reversing the polarity of one capacitor with respect to polarity of the other capacitor.

It is well known in the electrical arts that, when an uncharged electrical capacitor is connected directly across the terminals of a unidirectional source of potential, an electrostatic field is rapidly built up between conductive plates within the capacitor and the potential measurable between terminals of the capacitor approaches the potential of the source. It is also Well known that, if an electrical resistance is connected in series with the capacitor and if the resulting series circuit is connected across the terminals of said source, the magnitude of the potential measurable across the terminals of the capacitor approaches the potential of the source at an exponential rate according to the equation:

wherein Go is the voltage to which the potential of the uncharged capacitor rises in t seconds, E is the voltage of the source of potential from which the capacitor is charged, E=2.7l828 (the base of natural logarithms), C is the capacitance of the capacitor in microfarads, and R is the resistance of the resistor in megohms. When the foregoing equation is reduced to the form:

2 it may be readily shown that. if R, C, and E have constant finite values, cc must be zero when t is zero and 6c is greater than zero when t is greater than zero. In other words, when R, C, and E are constant, t is proportional to a function of cc and vice versa.

Many electrical systems utilizing the magnitude of the electrostatic potential built up across a fixed value of capacitance which is connected in series with a fixed value of resistance and a source of constant potential have been shown in the prior art as means for providing an indication of the magn tude of a period of time. While these systems have been satisfactory for some purposes, I have found that the results obtainable therefrom are not accurate under certain conditions. Particularly, this is true under conditions wherein the timing capacitor may be exposed to variable temperatures elevated above a normal calibration temperature. I have observed that. hen capacitors containing solid dielectric or solid dielectric impregnated with liquid dielectric are charged and are then momentarily short circuited by a conductor having negligible resistance. the potential measurable between the terminals of such capacitor is ouickly reduced to zero but. upon removal of the short circuit, a residual potential appears and is measurable between said terminals. Hereinafter, I may refer to this phenomenon as polarization hysteresis since it appears to be caused by polarization of molecules of the dielectric substance employed as spacing and insulating material between the conductive plates of these capacitors and the inability of the polarizable dielectric to become quickly depolarized. I have also observed that this phenomenon of polarization hysteresis is a gravated by chan es in tem erature of the timing capacitor. I have found that. when it is desired to measure accurately very short intervals of time. the absolute magnitude of the potential developed in a timing capacitor may be quite small. an appreciable portion of the charge may be held as bound charges in the dielectric, and these bound charges may ap ear as an appreciable addit onal part of the total potential in a second timing cycle if the bound charges are not com letely neutralized between successive timing cycles.

It is, therefore, one object of my invention to minimize objectionable eiTects attributable to polarization hysteresis in capacitors which are charged to a potential which is employed as a measure of a period of time.

It is another object of my invention to provide a novel sequence of steps for charging and discharging electrical capacitors which are employed as elements in precise electric timing devices.

A further-object ofrmy,invent-ionis-to provide an improved electrical system adapted .to "record or display a value which is a function of the length of a period of time.

Other and further objects ,of my invention will become apparent from :theffollonzing :description when read in conjunction with the accompanying drawing, in which 1 is an elementary circnitzrliagramrsymbolically illustrating the electrical'connectioncof elements which may be used in the practice of my invention;

Fig. 2 is a diagram symbolicallydllustrating the electrical circuit of a system embodying novel features of my invention for automatically' displaying or recording a value which is proportional 1 to the diiierence .in time between :successive events; and

flE-ig. 3 is a-graph -showing avpluralityzof curves illustrative of the: nature andsequence of signals appliedto elements ofthe system'nhown iniFig. 2.

In the several figures of the drawingdike numorals or letters;:where used, designate like parts.

Referring first to Fig. l;the .letterl designates a unidirectional soume of .substantially'constant potentiaL-such as a battery oielectrolytic cells or the equivalent. C1 and C2 .are :ccnventional electrical capacitors which, takentogether, .fOlIIl an'electrostatic storage device. It will :be'understood that each oi capacito-rs Crand'Czare preferably-made up of two or more electrically conductive plates spaced and insulated from: each other by a dielectric substance such as'mica, ceramic, paper or other suitablematerial. In order to obtain best results in'the practice of'my invention, capacitors C1 and "C2 "should 'be :as nearly identical, physically and structurally,xas possible. However, useful and satisfactory-resultswill be obtained if capacitors C1 and C2 contain similar dielectric substances and have substantially equal capacitances or "have values of capacitance within -about"5% of each other.

Capacitor C1 is connectedin parallel relation to capacitor C2 through switchingmeans 2 and the conductors 3 aud t. Switching means 2 'is preferably a conventional double-pole doublethrow switch or relay constructed and arranged so thatthe polarity, or terminals, of capacitor C1 may be quickly reversed with respect to the pol-- larity, orterminals; 01 capacitor C2. The parallel circuit, comprising capacitors C1 and C2 isconnected in series witha resistance Pt and thence to ,oppositeterminals of'the source or potential P by conductors 5 ands. Means, such as a switch or relay '3, is interposed in the series circuit comprising conductors '5 and t, resistance R, and capacitors C1 and C2 to provide means for initiatingand for terminating fiow of current from source P into capacitors C1 and C2. As will be more fully explained in conjunction withFig. 2, switch '5 and resistance R may be replacedby a suitable electron tube network which functions in a manner to provide a high resistance and a means for initiating and terminating iiow of current.

It'will be apparentthat, at'theinstantswitch l is closed to complete the series-circuit, current begins to flow through resistance R and slowly builds up an electrostatic 'field'between "conductive plates in capacitor C1 and between similar plates in capacitor :02. "This flow of currentwvill continue until switch 7 is opened, or until the electrostatic potential between terminals of paralleled capacitors C1 and C2 is equal to the potential of source P. Obviously, the relative values ot-resistance R and the eflective combined capacitanceofCi and Czjmay be so chosen with respect to the potential of source P that any desired length of time can be required to charge the capacitors ,Cl and C2 to a preassigned fraczticnacf the potentialof source P. As shown in "Fig. l l lprovide -.a high impedance meter 8, such as a vacuum tube voltmeter or a potentiometergzadartted to indicate or record the electrostatic potential :developed in the parallel cir- "euit ccmprisingcapacitors C1 and C2. Meter 8 may be connected across opposite terminals of :capacitor Gz..;by conductors 9 and it. Since the potential of source P is constant, meter 3 may be calibrated in units of time provided the value of resistance R and the values of capacitances C1 and 'Cr are constant.

"After a'charge hasibeen'built up'in capacitors Cyan-d C2, and after'the potential developed between the terminals thereof has been measured, itis necessary to dischargethe capacitors to zero potential-before"another charge, which will be proportional 'to thelength of the charging time, isplaced thereon. JAccordingly, a switch, relay, or equivalent means i! 1 is preferably provided, and maybe connec'te'dlto the terminals of capacitor Czby conductors 'l 2 andl3. When switch it is momentarily closed. a'major portion oiithe charge in capacitors'C1 and "C2 is .quickly discharged. Hereinaitenlhis portion of "the charge may be referred to as 'a readily 'dischargeable portion of the charge. ln accor'dance with'my observations,'-if switch t! -ison'ly momentarily closed, as it may be in a rapid timing cycle, charges' which arefirmlyiboundincapacitors C1 and C2, as by polarization 03f the dielectric therein, will notbe comp-letely d-isch-arged and thepotential measurable =across=the=terminals of capacitors C1 and C: will immediately begin .to rise upon opening switch H. "Therefore," in accordance with my invention, the polarity 0f capacitor C1 is thereafter reversed with respect-to the polarity of capacitor Czby means or switch 2. Any residualbound charge in capacitor 'C1 thereby instantly neutralizes a residual bound chargeofsubstantially equal ma nitude incapacitorCm and the effective potential across the parallel circuit-containing these capacitors is'instantly reduced to Zero or an excee inglysma'll value.

'Frorn the foregoingdescripticn it will become apparent that the advantages derivable from the methotl'and'apparatus of my'inventicn may also be obtained'when switching means ii is omitted. Thus, after capacitors "C1 and C2 have been charged to a desired extent and'the potential therein'hasbeen'measuredor utilized in meter switching-means? may' be operated to reverse the pclarity. of-capacitor 'Ci with respect'to the polarity of capacitor C2. .Bcththe readily dischargeable and the difficulty dischargeable-porticns of the charge in thesetcapacitors will then be neutralized instantaneously. In general, I prefer to "closeswitch H before operating switch 2 in those instances where capacitancesm and C2 are comparativelyflargepor where the actual potential'betweenthe opposite "terminals of these capacitors is comparatively high.

Turning now toiE ig. 2,1 have shown schematically and symbolically one embodiment of an portional to, the times between the occurrence of successive events, and adapted to repeat the timing cycle rapidly and automatically. In the drawing the numerals 2i and 22 designate means for receiving spaced impulses and converting these impulses to electrical pulses. Since means 221 and 22 may be any of a large number of wellknown means, details thereof are not shown. It will be understood, however, that means 2! and 22 may, for example, be devices adapted to receive acoustic impulses and to convert these impulses to sharp electrical pulses, or they may include photo-electric devices adapted to convert changes of intensity of light to electrical pulses. For purposes of illustration, it is assumed that pulse source 2i is always actuated before pulse source 22 so that sourceZl may initiate the timing of an event and source 22 may terminate said timing. The impulse produced by source M is preferably in the form of a sharp negative pulse which is applied through conductor 23, capacitor E l, and conductors 25 and 26 to the grid or control electrode 2? of a thermionic space charge device or vacuum tube T2. Similarly, the impulse produced by source 22 is also preferably in the form of a sharp negative pulse which is applied through conductor 28, capacitor 2% and conductor 30 to the grid or control electrode 3! of a thermionic space charge device or vacuum tube T1. The anode 32 of tube T1 is connected to the positive terminal of a source of direct current power P through a load resistance as and conductor 3%, while the anode 35 of tube is similarly connected to power source P through load resistors Eric, 3%, and conductor 3 The cathode Bl of tube T2 connected to common ground G and the negative terminal of power source P through a resistance 3% by-passed by a capacitor 39. Cathode 4d of tube T1 is connected to cathode 3', by conductors ii and 42 through the normally closed contacts 53 of a spring-return relay whose solenoid is designated by the numeral 44.

The anode 32 of tube T1 is coupied to control grid iii of tube T2 through resistor 45 having a capacitor ll shunted in parallel therewith. Similarly, the anode 35 of tube T2 is coupled to control grid iii of tube T1 through resistor 48 having a capacitor so shunted in parallel therewith. Control grids Ell and 35 are connected to common ground G through resistors 4t and 4%, respectively. As will be evident to workers in the art, tubes T1 and T2 and the networks associated therewith form a conventional Eccles-Jordan type of trigger circuit.

Output from anode 35 of tube T2 is taken from the junction between resistors 35a and 361) through conductor 5! and capacitor 52, and is applied to the control electrode or grid 53 of a thermionic space charge tube T3 which is arranged as a conventional cathode follower. The anode 5!! of tube T3 may be connected to power source P through conductors 55 and 34's. The cathode 58 thereof is connected to common ground G through resistors 52 and 58 in series. A suitable bias voltage is thereby provided for grid 5&3. A return path between grid 53 and cathode 56 is provided by a resistor 59 which connects grid 53 to the junction of resistors 5! and 58. Output energy may be taken from tube T3 across cathode resistors 57 and 58 through a coupling condenser 66 connected to cathode 55.

When a negative pulse from pulse source ii is applied to grid 2'! of tube T2, anode current in the latter is instantly cut off while flow of .anode current in tube T1 immediately begins 6. and continues until a negative pulse, derived from pulse source 22, is applied to grid 3| of tube T2. This latter pulse causes the anode current in tube T2 to be cut off. As a result of this action, an excitation voltage is superimposed upon the negative bias voltage applied to grid 53 of tube T3. This excitation voltage is in the form of a steeply rising and falling, substantially fiat crested, square wave signal whose crest value is positive with respect to the bias voltage. The duration of the square wave crest is substantially equal to the difference in time between the pulse formed in pulse source 2i and that formed in pulse source 22.

The output energy derived from cathode 56 of tube T3 is also in the form of an identical square Wave signal and this output energy is applied through capacitor 60 to the control electrode or first grid SI of a conventional pentode type thermionic space charge device or vacuum tube T4 having a cathode 62, a second or screen grid 63, a third or suppressor grid 64, and an anode 65. Grid 64 and cathode G2 are joined together by a conductor 66 either internally or externally of tube T4. Cathode 62 is connects: to common ground G through a suitable resistance 67 while grid 64 is connected to the positive terminal of power source P through a suitable resistance 55. Control element 6! may be connected to common ground G through a resistance E9. The anode 65 of tube T4 is connected through a conductor 10 to one terminal of a capacitor C2 and through a conductor H to one terminal of a voltage utilization device, such as a conventional recording potentiometer or vacuum tube, voltmeter represented in the drawing by the symbol M. The second terminal of capacitor C2 is connected through a conductor F2 to the other terminal of device M and to the positive terminal of a source of substantially constant unidirectional potential. In Fig. 2 of the drawing this source of potential is shown as the anode it of a conventional cold cathode, gas-filled voltage regulating device or tube Ts which may be connected to the positive terminal of power source P through a suitabl voltage dropping or current limiting resistance 14. The cathode i5 of tube T9 is joined to the negative terminal of source P through common ground G. It will be understood that any other suitable source of unidirectional constant potential, such as a battery of voltaic cells, may be substituted for the source shown provided the polarity of the source and constancy of the potential is maintained.

In accordance with my invention, a second capacitor C1 having substantially the same capacitance as capacitor C2 is connected in parallel. with the latter through conductors Hi and. .42. A double-pole, double-throw switching device, such as a fast acting, stepping relay. whose solenoid is designated by the numeral '58, is arranged in conductors and l'] so that the terminals or polarity of capacitor C1 may be quickly reversed with respect to the terminals or polarity of capacitor C2, as indi ated schematically in the drawing. It will be apparent to workers in the art that the aforementioned stepping re. preferably of the type wherein a first energnu tion of the solenoid causes the switch cent as thereof to move into a first position and remain there after de-energization of the solenoid and a second energization causes the switch contacts to move to a second position and remain there after de-energization.. It willalso be apparent to workers :in :the tart that, under some conditions, the aforementioned stepping relay may be replaced by a double-pole, "double-throw, spring return relay, butresults obtained therewith generally will not be as satisfactory as with the stepping type of relay.

To provide a necessary operating potential within tube Tr, grid 63 thereof is connected through a'conductor 79 to the positive terminal of a source of unidirectionalpotential such as is derivable'through conductor '32 or conductor 34. When a positive'excitation voltage, such as isderived'fromthe square wave output of T3, is superimposed upon the normal bias voltage applied to grid-6i of'tube T4, the'latter tube behaves like'a variable rcsistance'adapted to pass current at a constantdate. Under these conditions an electrostatic potentialis caused'tobuild up at a substantially constant rate across the terminals'of capacitor C2 and capacitor C1 in parallel therewith. When the amplitude of the excitation voltageapplied to grid Eil suddenly drops back to the initial bias condition, the anode cathode impedance of tube T4 becomes al most infinite and capacitorsCi and C2 no longer build up additional potential. Meter device M thereafter will indicatethe maximum potential developed in-capacitors C1 and C2 and this potential will be proportional to the precise time of current flow through-tube T4 (and hence to the precise difference in timing between the pulses iormedinpulse-sources-2i and 22) providedthe initial potential in capacitors C1 and C2 is Zero.

So that the potential developed in capacitors C1 and C2 may be automatically reduced to zeroat the end of a timing'cycle, I provide an electronically controlled-switchingcircuit which may be triggered by electrical pulses formed in source 2! or source 22. InFig. 2 I have shown the actuation of the switching circuit as being initiated bya pulse derived from source 22. As may be seen from thedrawing, a portion of the pulse energyfrom source 2-2 is'applied through a conductor'Bt'i and capacitorBl to the anode 32 of a thermionic space charge'device or vacuum tube T5 and, thence, through a capacitor 33 to the control electrode o grid 84 of a similar tube T6. The cathodes 85 and 880i tubes T5 and Te, respectively, are joined together by a conductor Si and are connected to common ground G through a suitable resistance 88. Control element or grid 3% of tube T5 is provided with a suitable fixed bias potential by connection to an intermediate point on a voltage divider made up or" resistance elements ill ands! which are connected in series between common ground G and a conductor 92 leading to the positive terminal of power source P. Controlelement -8 oftube T6 is-biased at a positive potential by connection to a resistance element- 93 which may be connected to the positive terminal of power source P through conductor '92. Anode 82 of tube T5 and anode M of tube T5 are connected to conductor Q2 and the positive terminal of power source P through anode load resistance elements 9'5 and 9%, respectively.

Upon consideration of the circuit including tubes T5 and T's it may .beseen that anode .current flows through tube T6 and its cathode resistance element diiwhen the circuitis in its nor mal equillbriumcondition. The constants of the circuit'may'be so chosenthat tube T5 is cut on;

in this equilibrium conditionbecauseof the bias voltage which is developed :across resistor 88 til when plate currentisflowing in tube Te. :As will be apparent to those familiarwith flip-flop-circuitsof this type, tubes T5 and T5 should-conduct successively but should not pass current at the same time. If plate resistors 95 and 96 were of the same magnitude, a substantially constant voltage would appear across cathode resistor 88 as a result of plate current through tube T6 during one portion of'the cycle and as a result of a like current through tube T5 during the remainder of the cycle. In order that the signal obtained from cathode resistor 88 may assume a rectangular wave shape the plate resistors 95- and it are made unequal in size and I prefer to make resistor 95 considerably larger than resistor 96 so that a smaller voltage will appear across resistor 88 while tube T5 is conducting than is the case when tube To is conducting. To follow the sequence of operations in thiscircuit, consider first that tube To is conducting and tube T5 is nonconducting. When .a short negative pulse derived from source 23 is applied to grid 3% through capacitors SI and 83, the flow of anode'current in tube To is momentarily reduced to zero. Asa result of this action, the potential across resistor 88 drops to zero which has'the effect of removing the cut-off bias previously applied between grid 39 and cathode 85 or tube T5 enabling said tube to pass plate current. As soon as tube T5 begins to conduct, its plate voltage will be abruptly lowered and this reduction in voltage will be applied to grid E2 3 of tube To through condenser 83. This will maintain tube To in cut-ofi condition until condenser 33 has time to discharge through resistors 83 and 95, thereby allowing grid 84 to become increasingly positive in exponential fashion until tube T6 again becomes conducting, thereby raising the voltage across resistor 88 and rendering tube T5 nonconducting as was the case with the assumed original condition of the circuit. As a result of the above described action, the potential across resistor t3, when plotted against time, takes on substantially the form'of a rectangular wave signal having a negative, or less positive, portion which endures for an interval governed by the time required for capacitor 83 to discharge through resistance elements 93 and 95. This rectangular wave signal is impressed across a difierentiating network comprising a relatively small capacitance 9? and small resistance 98. Thel'esulting differentiated signal thereafter is superimposed upon a negative bias voltage, supplied by suitable means such as a battery 99, applied to grid element Hill of a gasfilled, thermionic space charge device or'thyratron T7. lhe positive pulse of the differentiated signal triggers discharge of anode current between anode Hll and cathode N32 or" tube T1. Cathode I82 is connected tocommon ground G through a conductor Hi3 and relay solenoid M. The how of anode current in thyratron T7 causes relay is to be actuated so long as sufiicient current flows therethrough. However, anode m1 receives a positive potential from a relatively large capacitor lil l, one of whose terminals is tube T7 rapidly discharges capacitor lu Lwhereupon continued flow of current-ceases untilcapacitor lo l becomes recharged and anothertrig- .igering pulse is applied to grid we.

The spring-return type relay operated'by'solenoid '44 includes normally-closed contacts 43,

9 normally opened contacts I06, and double-throw contacts I 01a and IO'Ib, the former of which is normally closed by contact with a switch arm I 010. As has been mentioned hereinbefore, contacts 43 are connected through conductors II and 42 to the cathodes 40 and 31 in tubes T1 and T2. The normally-opened contacts Ice are connected through conductors I6 and I? to opposite terminals of capacitor C1 and thence through conductors 'II and I2 to opposite terminals of C2. The contact IU'Ia connects through a resistance element I08 to conductor 92 and the positive terminal of power source P, while contact IOIb is connected to the grid element I09 of a thyratron T8 and through a resistance element I I!) to common ground G. The switch arm IOIc, which may contact either I07a or ID'Ib, is connected to one terminal of a capacitor III whose other terminal is grounded at G. Thus, when no current flows through solenoid 44, the cathodes 31 and 40 are connected together, capacitors C1 and C2 are not short circuited, and capacitor III is connected to receive a charge from source P through resistance element I08. On the other hand, when current is caused to flow through solenoid 44, contacts t3 are caused to open, thereby insuring that tube T2 is made initially conductive for the next timing cycle, contacts I 08 are caused to close, thereby momentarily short circuiting the terminals of capacitors C1 and C2, and switch arm Iiiic is moved from contact IU'Ia to IOTb, thereby applying the charge in capacitor I Ii to grid element Hi9 in thyratron Ts, triggering a flow of anode current therein.

The cathode II2 of thyratron Ta is connected by conductor H3 to the solenoid I8 and thence to common ground G. The anode I I4 of thyratron T8 is connected to one terminal of a capacitor H5, whose other terminal is grounded at G, and to a resistance element IIE which may connect through conductor 92 to the positive terminal of power source P.

When the flow of anode current through thyratron Ta is triggered by application of the charge in capacitor III to grid I09, this anode current flows through solenoid I8 and causes operation of the stepping relay contacts whereby the terminals, or polarity, of capacitor C1 are reversed with respect to the terminals, or polarity, of capacitor C2, and any charges bound into the dielectric material of these capacitors are immediately neutralized. The flow of anode current in tube T8 rapidly discharges capacitor II5, whereupon continued flow of current ceases until the capacitor becomes recharged and another triggering voltage from capacitor III is applied to grid 169.

The sequence of operations, above described, may be more easily understood by reference to Fig. 3 wherein I have shown a composite graph indicating the idealized nature and the sequence,

T1Tr, and Te-Ts shown in Fig. 2. Upon the same graph I have also shown a curve representing the potential measurable across capacitors C1 and C2 as it might appear upon a record produced by recording voltmeter M.

In Fig. 3 the abscissae represent uniform units of time, which may be expressed in seconds or microseconds, whereas the ordinates represent arbitrary units of potential more positive or more negative than an equilibrium potential upon the element under consideration, except in the case of the bottom curve wherein the ordinates rep- 10 resent differences in arbitrary potential units between terminals of the capacitors C1 and C2.

The first, or upper, curve of Fig. 3 is designated by the numeral 2M and represents a series of sharp negative pulses applied by pulse source ZI to the grid element 27 of tube T2. It may be seen that, for purposes or" illustration, pulses are shown occurring after total elapsed time of 2, 8,

4 and 20 units. As mentioned hereinbefore, these pulses, acting through tubes T1-T4, initiate flow of current into capacitors C1 and C2.

The second curve is designated by the numeral 202 and represents a series of sharp negative pulses applied by pulse source 22 to the grid element (ii of tube T1. The pulses are shown occurring after total elapsed time of 6, 9, l6, and 23 units. These pulses, acting through tubes T1-T4, cause termination of the fiow of current into capacitors C1 and C2.

The third curve, designated by the numeral 233, represents the signal derived from the anode 35 of tube T2 and applied to the grid elements 53 of tube T3. It may be seen that when tube T2 is made non-conductive, as a result of the application of a negative pulse to the grid element thereof, the signal applied to the grid 53 in tube T3 swings positive and remains substantially steady until tube T2 is again made conductive as by the application of a negative pulse to the grid element of tube T1. Reference to Fig. 3 shows this effect wherein, at the instant the first pulse appears on curve 2M, the signal applied to the grid of tube T3 swings abruptly in a positive direction and then remains constant until the instant when the first pulse appears on curve 2532, at which time the signal again swings abruptly in a negative direction. The substantially fiat positive crest of the resulting square wave thus endures throughout the interval between the first pulse on curve 24M and the first pulse on curve 232.

Since the function of tube T3 is to produce an output signal which is a faithful reproduction of its input signal, but at a different impedance, it is apparent that the signal app-lied to the grid element of T4. is substantially identical to the signal applied to the grid of T3. This is shown by the fourth curve designated by the numeral 26:1 in Fig. 3.

Also, since the signal applied to the grid element 84 of tube T6 is identical to that applied to the grid element of tube T1, the timing and nature of these signals should be identical. This is shown by the curve 2&5 in Fig. 3.

The sixth curve, designated by the numeral 288, represents the potential drop across resistance element 38 which is common to the cathodes of both tubes T5 and T6. By comparison of curve 238 with curve 265 it may be seen that, when a negative pulse is applied to the control grid of tube T6, the potential across resistance element 88 abruptly swings in a more negative direction to a certain crest value and remains substantially at said value for a brief interval before swinging back abruptly to an equilibrium value. The duration of the crest is governed by the time constant of the resistances 93 and c5 and the capacitance B3.

The curve designated by the numeral 281' represents the signal applied to the grid of thyratron T7. As may be seen from a comparison of curves 2% and 28?, the signal applied to the grid of thyratron T2 is in the form of a sharp negatively peaked signal followed by a sharp positively peaked signal, said peaks occurring sub acsaoro stantially simultaneously with the fall and rise of potential'across the resistance element 83 in the cathode circuit oitubes T- and Te. As is evident to workers in the art, it is the positive peak of the signal applied to the grid of thyratron T7 which triggers the how of anode current therein. The delay in the generation of this positive peak as compared with thetime of arrival of a pulse applied to the grid element of tube To (curve 2%) is governed by the time constant of capacitance t3 and resistance elements 93 and 95; This time constant is preferably made only sufficiently long to insure that meter M has time to record accurately the potential across capacitors C1 and C2.

The eighth curve, designated by the numeral j8,,shcws the signal-applied to the grid element ofthyratronTa It may be seen that this curve comprises a series of positive pulses which occur slightly laterthan the positive pulses shown in curve 28?; As has been mentioned hereinbefore, the signal'applied to the grid of tube Ta is derived by'theapplication or the charge in capacitor 1 l i to the grid iiifi'through relay contacts iillb and 610; The delay between the positive peaks of curve 2! and curve 2% is due to unavoidable mechanical delay in actuation of contacts in relay M. So that this delay may be as short as possible, relay M should-be a selected fast-acting relay.

Theninth, or lower, curve in Fig. 3 is designated generally by the numeral 209 and represents the'potential measurable across timing capacitors Cl and C2 in parallel. Upon comparison of curve 209' with curves Elli- 2st, inclusive, it may be seen that-at the instant of arrival of a pulse which is applied to the grid 2? of tube T2 (curve 28H the potential across capacitors C1 and C2 begins to rise-substantially linearly until the instant Of arrival of a pulse which is applied to the grid 3i of tube T1 (curve 262). The potential across capacitors C1 and C2 will then remain substantially constant until relay Mi has been actuated, thereby closing contacts tilt-which short circuit the terminals of capacitors C1 and C2 simultaneously. The-length of time during which contacts mt remain closed is governed in part by the mechanicalconstructionof relay fi l and, more important- 1y, by the time constant of capacitance EM and resistance I05 in the anode circuit of thyratron T7. For purposes of illustration, it has been assumedthat this time constant is very small and the mechanical release of contacts 106 in relay 44 very fast so that the potential across capacitors Grand C2 drops to zero substantially instantaneously as indicated by portions of curve 269 designated by the numeral 2 i ii. 7

subsequent to the opening of contacts H36, I have found that the potential across capacitors C1 and C2 begins to rise at a rate proportional to the magnitude of the previous charge as represented by portions of curve 20% designated by the numeral 2! 1. Even if the short circuit produced by'closing contacts N36 is maintained for a considerable length of time, I have found that the potential produced by charges bound up in capacitors C1 and C2, as by polarization of the dielectric, are not completely neutralized and the error resulting from slow release of these charges maybe an appreciable fraction of a small potential which it is desired to measure accurately. The broken line 2 I 2, shown adjacent curve 289 in Fig. 3, illustrates the nature of the error which maybe introduced as a result of polarization hysteresis in a capacitor employed in .precise timing circuits; If the magnitude of thepotentialdeveloped across capacitors C1 and-C2 as a result-of charges bound intothe dielectric was the same at the end of each timing measurement, it-could be compensated for in subsequent calculations. However, this magnitude changes with different temperatures and with different intervals of time and cannot, therefore, be readily compensated. By reversing the polarity of capacitor C1 with respect to the polarity of C2, charges bound into the dielectric of each of these capacitors neutralize each other and the potential measured across these capacitors thereafter returns to zero asindicated by the portions 2H3 of curve 2% Comparison of curves 288- and. 28 9" Will-show that the portion 213 of'curve 2W lags somewhat behind thepulse which triggers thyratron Ts-and thereby actuates relay l8; This-delayrepresents mechanical delay in the actuation of contacts in rel-ay'lS. Itwill be apparent, therefore, that -in a device intended to record the timing ofxevents in rapidly repeated cycles, relay it must be selected to introduce negligible time delay between excitation of the solenoid therein and the resulting mechanical movement of the switching contacts.

From the foregoing description of Figs. 2 and- 3, it may be seen that lhave provided an electrical timing network having a constant potential source of unidirectional energy P, first andsecond capacitors C1 C2 connectedinparallel, switching means arranged to reverse polarity ofthe first capacitor with respect tothe polarity of the second capacitor, a resistance value comprising: the anode-cathode path of-"t'ube reconnected in series between the parallel circuit of capacitors C1 and C2 and the source P, and means comprising. grid element iii of tube Tifor selectively initiating'and terminating flow of current into capacitors Grand C2. It may also'be seen that, through the provision of'pulse sources 2! ands22, the 'networhsxassociated with tubes 'I1-T3, andthe networks-and relays associated with tubes T5Ts, IJhaveprovided means for controlling a sequence of steps a which includes initiatingfiow. of energy'into capacitors Ci and'C2, terminating. saidfiow of'enorgy, and subsequently: reversing polaritywf capacitor G1 with respect to capacitor C2.

It willbe apparent to workers skilledzinztheart that many changes maybemade in specific;-embodiments shown herein for illustrative purposes without departing from: the spirit: and: scopeof the appended claims.

Having described andiillustrated my invention, what-I claim as novel. and'desireto secure by Letters Patent is:

l. A method for neutralizing polarization=h-ysteresis in an electrostatic energy storage, device carrying an electrostatic charge upon aplurality of conductive plates havingipolari'zable dielectric material.therebetween whichincludes the steps of discharging a readily dischargeable portion ofsaid charge and thereafter connecting. the plates in substantially one-half of said. device directly and in reversed polaritytotheiplatesin another half thereof.

2. Inamethod for measuring a periodzof'tiine wherein a unidirectional. currentiis continuously flowed from a source of constant potential through a resistance in series therewith andis continuously during said period in. an electrostatic energy storage device comprisingxa plurality of conductive plates and aplurality: of polarizable dielectric memberstherebetween, and wherein the: magnitude ofthe. electrostatic potential developed in said storage device during said period is utilized as a measure of the duration of the period, the improvement which in cludes the sequen e of steps of utilizing said electrostatic potential and, thereafter, connecting the plates in one-half of storage device directly and in reversed polarity to th plates in another half thereof.

3. In a method for measuring a. period of time wherein a unidirectional current is continuously flowed from a source of constant potential through a resistance in series therewith and is continuously stored during said period in an electrostatic energy storage device comprising a plurality of conductive plates and a plurality of polarizable dielectric members thereloetween, and wherein the magnitude of the electrostatic potential developed in said storage device during said period is utilized as a measure of the duration of the period, the improvement which includes the sequence of steps of utilizing said elcc trostatic potential. thereafter discharging from said device a readily dischargeable portion of said potential, and then connecting the plates in substantially one-half of said storage device directly and in reversed polarity to the plates in another half thereof.

4-. An electrical network comprising a substantially constant potential source of unidirectional electric energy, first and second electrical capacitors having substantially equal values of capacitance, means directly connecting said first capacitor in parallel to said second capacitor to form a parallel circuit, said means including switching means constructed and arranged to reverse selectively the polarity of connection of said first capacitor to said second capacitor, means electrically connecting said parallel circuit in series with said source of energy, means for selectively initiating and terminating a flow of energy from said source into said parallel circuit whereby an electrostatic field is formed in said 14 capacitor, and means for discharging a readily dischargeable portion of said electrostatic field.

5. An electrical timing network comprising, in combination, a substantially constant potential source of unidirectional electric energy, first and second capacitors comprising polarizable dielectric material and having substantially equal values of capacitance, means directly connecting said first capacitor in parallel to said second ca pacitor to form a parallel circuit, said means including switching means constructed and arranged to reverse selectively the polarity of connection of said first capacitor to said second capacitor, means electrically connecting said parallel circuit in series with said source of energy, said last-mentioned means including a selected resistance value electrically connected in series with said source and said parallel circuit, means for selectively initiating and terminating a flow of energy from said source into said parallel circuit, means electrically connected in parallel with said capacitors for utilizing energy stored therein, and means for discharging a readily dischargeable portion of energy stored in said capacitors.

6. A network in accordance with claim 5 including, in combination, means for controlling the sequence of steps comprising initiating flow of energy, terminating said flow, discharging readily dischargealole energy, and subsequently reversing polarity of said first capacitor with respect to said second capacitor.

CHARLES J. CHARSKE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,384,829 Garstang Sept. 18, 1945 2,384,831 Garstang Sept. 18, 1945 2,534,043 MacPhail Dec. 12, 1950 

